The present invention relates to a discharge lamp having an inner arc tube and outer jacket, and particularly to a discharge lamp designed to operate at a high tube loading.
For the ultraviolet light source of apparatus for physics and chemistry, for example a fluorescence detector in a liquid chromatograph, there have been used conventionally deuterium lamps or xenon short-arc lamps. The detection limit of these apparatus is dependent on the radiance of the light source, and the analysis of an extremely small amount of material needs a high radiant light source operable stably for continuous discharging. Deuterium lamps of around 30 watts are commonly used, but their ultraviolet radiance is not high enough for the analysis of an extremely small amount of material. Although large power deuterium lamps are available to cope with this matter, they have drawbacks such as the bulkiness due to their increased power dissipation and the need of water-cooled structure. Xenon short-arc lamps provide a high ultraviolet radiance, but have shortcomings such as a poor stability of intensity and a short work life of around 150 hours.
An alternative high radiance ultraviolet light source is the metal halide lamp filled with tantalum halide (disclosed in Japanese Patent Application Laid-Open No. 52-45391 filed on Apr. 9, 1977). However, the metal halide lamp designed for this high loading purpose operates at a tube temperature as high as 1000.degree. C., that causes a swell of the arc tube in the operation if any little impurity is included within the tube during the fabricating process or if the electrode has any small bend.